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PubMed1992

Frictional coefficients of ion-implanted alumina against ion-implanted beta-titanium in the low load, low velocity, single pass regime.

The frictional coefficients were measured for four wire alloys against the flats of polycrystalline alumina cylinders using a low load, low velocity, single pass device. Ion-implantations of titanium into polycrystalline alumina flats and nitrogen into beta-titanium wires reduced the static and kinetic coefficients from 0.50 and 0.44 before implantation to 0.20 and 0.25 after implantation, respectively. These results are similar in magnitude to frictional coefficients for unimplanted, control couples of stainless steel, cobalt-chromium, and nickel titanium wires against polycrystalline alumina flats. For orthodontic applications, we conclude that more efficient and reproducible appliances can be engineered for tooth movement if ion-implantation is used to reduce the abrasion of beta-titanium by polycrystalline alumina.

Aluminum Oxide↗

PubMed1989

Coefficient of static friction at pig femoral osteotomies: the role of anatomic reduction and compression on the value of the coefficient.

The coefficient of static friction for pig femora following an osteotomy has been determined in vitro. It was found that the coefficient had a value of 0.46 +/- 0.05, and that this was independent of the reduction force applied to the osteotomy site, provided there was good anatomical reduction. When the osteotomy was not anatomically reduced, the coefficient of friction varied in a linear manner with the applied reduction force.

Animals↗

PubMed1989

Frictional response of articular cartilage containing crystals.

Many joint diseases are associated with the deposition of crystals in articular cartilage. Three main types are commonly found: calcium pyrophosphate, calcium hydroxyapatite and monosodium urate. The effects of these articular crystals on the frictional properties and the surface condition of the articular cartilage were studied. A total of 43 cartilage specimens cut from 19 post-mortem knee joints have been tested in purpose-designed apparatus. The results show that a high friction coefficient and a high level of crystal deposition tend to occur with a worsening of the surface quality of the articular cartilage.

Biocompatible Materials↗

PubMed1995

The friction cost method for measuring indirect costs of disease.

A new approach for estimating the indirect costs of disease, which explicitly considers economic circumstances that limit production losses due to disease, is presented (the friction cost method). For the Netherlands the short-term friction costs in 1990 amount to 1.5-2.5% of net national income (NNI), depending on the extent to which short-term absence from work induces production loss and costs. The medium-term macro-economic consequences of absence from work and disability reduce NNI by an additional 0.8%. These estimates are considerably lower than estimates based on the traditional human capital approach, but they better reflect the economic impact of illness.

Absenteeism↗

PubMed2004

Vehicle speed affects both pre-skid braking kinematics and average tire/roadway friction.

Vehicles decelerate between brake application and skid onset. To better estimate a vehicle's speed and position at brake application, we investigated how vehicle deceleration varied with initial speed during both the pre-skid and skidding intervals on dry asphalt. Skid-to-stop tests were performed from four initial speeds (20, 40, 60, and 80 km/h) using three different grades of tire (economy, touring, and performance) on a single vehicle and a single road surface. Average skidding friction was found to vary with initial speed and tire type. The post-brake/pre-skid speed loss, elapsed time, distance travelled, and effective friction were found to vary with initial speed. Based on these data, a method using skid mark length to predict vehicle speed and position at brake application rather than skid onset was shown to improve estimates of initial vehicle speed by up to 10 km/h and estimates of vehicle position at brake application by up to 8 m compared to conventional methods that ignore the post-brake/pre-skid interval.

Automobile Driving↗

PubMed2005

A 15- to 25- year follow-up study of primary Charnley low-friction arthroplasty: a single surgeon series.

Long term outcome studies are essential to determine the effectiveness and durability of a procedure. We report our 15 to 25 year clinical and radiographic follow-up with the Charnley low-friction hip arthroplasty. Four hundred and forty-seven primary Charnley hip arthroplasties were performed by a single surgeon. Ninety-eight of the 447 hips from 75 patients were available for follow up at average of 18.9 years (range 15.3 to 25.4 years). Seventy-two hips (73.5%) survived clinically. Of these 72, seventy-one stems (98.6%) and 60 sockets (83.3%) survived radiographically. Kaplan-Meier survival analysis on all 447 hips using revision as an endpoint revealed 66.2% +/- 5.7% survival at 20 years. Twenty-six hips were revised. The main reason for revision was failure of the socket. Complications included dislocation (3 of 98 hips), heterotopic ossification (7 of 98 hips), trochanteric wire breakage (6 of 98 hips), and trochanteric non-union (1 of 98 hips). Charnley low-friction hip arthroplasty is an effectiveand durable procedure. Key words: hip, arthroplasty, charnley, follow-up.

Adolescent↗

PubMed2005

Inter-segmental coordination: motor pattern in humans stepping over an obstacle with mechanical ankle joint friction.

This study examined the influence of a mechanical perturbation of the ankle joint on obstacle avoidance pattern. A decoupled control between the distal joint and the combined (hip-knee) proximal joints was observed according to the task requirement. In this context, a greater mechanical friction at the ankle should be compensated at this joint (local compensation) or alternatively, by regulating more combined proximal joints (knee and/or hip). The leading limb inter-segmental coordination was evaluated in both no constraint and constraint conditions in calculating ranges of motion (ROM), moments of force and powers (from heel-off to obstacle) at the ankle, knee and hip joints. Electromyographic activities were also analyzed. With the constraint, the dorsiflexor moment and the tibialis anterior activity remained unchanged while both ROM and power bursts (absorbed and generated) decreased. The hip and knee ROM remain invariant. At heel-off the absorption by hip extensors decreased and the forthcoming generation by knee flexors increased in the constraint condition. To quantify the inter-joint coordination, principal component analysis was used and indicated a high level of inter-joint coupling (synergy) that decreased with the constraint (i.e. less inter-joint coupling). At the ankle joint, the results suggest that the central command was the same in both conditions thus, not be adapted. At both the hip and knee joints, a combined joints modulation occurred to overcome additional friction.

Adaptation, Physiological↗

PubMed2007

Iliotibial band friction syndrome--a systematic review.

Iliotibial band friction syndrome (ITBFS) is a common injury of the lateral aspect of the knee particularly in runners, cyclists and endurance sports. A number of authors suggest that ITBFS responds well to conservative treatment, however, much of this opinion appears anecdotal and not supported by evidence within the literature. The purpose of this paper is to provide a systematic review of the literature pertaining to the conservative treatment of ITBFS. A search to identify clinical papers referring to the iliotibial band (ITB) and ITBFS was conducted in a number of electronic databases using the keyword: iliotibial. The titles and abstracts of these papers were reviewed to identify papers specifically detailing conservative treatments of ITBFS. The PEDro Scale, a systematic tool used to critique randomized controlled trials (RCTs), was employed to investigate both the therapeutic effect of conservative treatment of ITBFS and also to critique the methodological quality of available RCTs examining the conservative treatment of ITBFS. With respect to the management of ITBFS, four RCTs were identified. The interventions examined included the use of non-steroidal anti-inflammatory drugs (NSAIDs), deep friction massage, phonophoresis versus immobilization and corticosteroid injection. This review highlights both the paucity in quantity and quality of research regarding the conservative treatment of ITBFS. There seems limited evidence to suggest that the conservative treatments that have been studied offer any significant benefit in the management of ITBFS. Future research will need to re-examine those conservative therapies, which have already been examined, along with others, and will need to be of sufficient quality to enable accurate clinical judgements to be made regarding their use.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1989

The friction sweat test as a new method for detecting facial anhidrosis in patients with Horner's syndrome.

Forty-eight patients with Horner's syndrome documented by cocaine test were examined with the friction sweat test, a method of detecting a mild sweating asymmetry using alcohol and a standard office prism bar. In all but one patient, the results of the friction test corresponded with the results predicted by the history, physical examination, and Paredrine testing, or with the results of a starch-iodine sweat test. The test is a quick, simple, and reproducible procedure that allows a more accurate determination of the location of the Horner's syndrome at the initial office visit, and therefore assists in determining what tests need to be performed in the further examination of the patient.

Face↗

PubMed1995

Calculation of translational friction and intrinsic viscosity. I. General formulation for arbitrarily shaped particles.

A general method for calculating translational friction and intrinsic viscosity is developed through exploiting relations between hydrodynamics and electrostatics. An approximate relation xi = 6 pi eta 0C between the translational friction coefficient xi of a particle (eta 0: solvent viscosity) and its capacitance C was derived previously. This involved orientationally preaveraging the Oseen tensor, but the result was found to be very accurate. Based on preaveraging, we find that the intrinsic viscosity [eta] of a particle can be estimated from its polarizability alpha through [eta] = 3/4 alpha + 1/4 Vp, where Vp is the volume of the particle. Both the capacitance and the polarizability can be obtained in a single calculation using the boundary-element technique. An efficient approach is thus found for estimating [eta], a quantity that is very useful in practice because of its sensitivity to particle shape but is notoriously difficult to calculate. Illustrative calculations on ellipsoids, cylinders, and dumbbells demonstrate both the accuracy of the approximate relations and the efficiency of the present method.

Computer Simulation↗

PubMed1995

Calculation of translational friction and intrinsic viscosity. II. Application to globular proteins.

The translational friction coefficients and intrinsic viscosities of four proteins (ribonuclease A, lysozyme, myoglobin, and chymotrypsinogen A) are calculated using atomic-level structural details. Inclusion of a 0.9-A-thick hydration shell allows calculated results for both hydrodynamic properties of each protein to reproduce experimental data. The use of detailed protein structures is made possible by relating translational friction and intrinsic viscosity to capacitance and polarizability, which can be calculated easily. The 0.9-A hydration shell corresponds to a hydration level of 0.3-0.4 g water/g protein. Hydration levels within this narrow range are also found by a number of other techniques such as nuclear magnetic resonance spectroscopy, infrared spectroscopy, calorimetry, and computer simulation. The use of detailed protein structures in predicting hydrodynamic properties thus allows hydrodynamic measurement to join the other techniques in leading to a unified picture of protein hydration. In contrast, earlier interpretations of hydrodynamic data based on modeling proteins as ellipsoids gave hydration levels that varied widely from protein to protein and thus challenged the existence of a unified picture of protein hydration.

Algorithms↗

PubMed1997

Manipulation of individual viruses: friction and mechanical properties.

We present our results on the manipulation of individual viruses using an advanced interface for atomic force microscopes (AFMs). We show that the viruses can be dissected, rotated, and translated with great facility. We interpret the behavior of tobacco mosaic virus with a mechanical model that makes explicit the competition between sample-substrate lateral friction and the flexural rigidity of the manipulated object. The manipulation behavior of tobacco mosaic virus on graphite is shown to be consistent with values of lateral friction observed on similar interfaces and the flexural rigidity expected for macromolecular assemblies. The ability to manipulate individual samples broadens the scope of possible studies by providing a means for positioning samples at specific binding sites or predefined measuring devices. The mechanical model provides a framework for interpreting quantitative measurements of virus binding and mechanical properties and for understanding the constraints on the successful, nondestructive AFM manipulation of delicate samples.

Aluminum Silicates↗

PubMed2001

Phenomenological study of the bed--wall friction in axially compressed packed chromatographic columns.

The properties of column beds prepared with slurries of Kromasil C8 in 12 different solvents, using the same axial compression skid, were investigated. The extent of the consolidation of the column beds, their permeabilities, and the friction shear stress of these beds against the column wall were determined, as well as the column efficiencies (for an unretained tracer). The results of this study illustrate the influence of the wall effect on the consolidation. The permeability of columns consolidated under a constant compression stress was found to increase with increasing bed length. The bed-wall friction shear stress increases rapidly with increasing bed length and varies widely with the nature of the solvent used. No correlation was found between this shear stress and any physico-chemical property of the solvent. The best efficiency was observed for a column consolidated from a slurry in ethanol.

Chromatography, Liquid↗

PubMed2002

Capillary electrophoresis in aqueous-organic media. Ionic strength effects and limitations of the Hubbard-Onsager dielectric friction model.

The mobilities of three aromatic sulfonates, ranging in charge from -1 to -3, were investigated by capillary electrophoresis using buffers containing 0 to 75% ethanol or 2-propanol. Absolute mobilities were determined by extrapolation of the effective mobilities to zero ionic strength according to the Pitts' equation. For all buffers studied, ions of higher charge experienced larger ionic strength effects. The resulting ionic strength-induced selectivity alterations were more dramatic when organic solvents were present in the media. Furthermore, for different organic modifier types and contents, the magnitude of the ionic strength effect was governed to a large extent by the 1/(eta epsilon 1/2) dependence in the electrophoretic effect of the Pitts' equation. Addition of ethanol or 2-propanol to the electrophoretic media resulted in changes in the absolute mobilities of the ions. These solvent-induced mobility changes are attributed to dielectric friction. As predicted by the Hubbard-Onsager model, dielectric friction increased with increasing organic content and with increasing analyte charge. As a result, dramatic changes in the relative absolute mobilities were observed, such as a reversal in migration order between sulfonates of -1 and -3 charge in 75% 2-propanol. Within the alcohols, the Hubbard-Onsager model was successful at predicting the relative mobility trends upon changing solvent. However, the relative trends observed between acetonitrile-water and alcohol-water media were not consistent with the model. This may be explained by the continuum nature of the model, whereby the different ion-solvent interactions characteristic to each solvent class are not taken into account.

Electrophoresis, Capillary↗

PubMed1990

Molecular friction in an actomyosin molecular machine.

In muscle contraction, it has been widely recognized that a binding state exists between myosin and actin in the presence of Mg-ATP. To estimate the magnitude of binding strength, I introduce a concept of frictional phenomena which occurs between two sliding bodies in contact each other. In such cases, the sliding speed can be formulated as a function of the actin-myosin bond strength. In order to validate this, the present theory is applied for the two movement assay systems with no external load; one movement assay of Phalloidin Rhodamine bound F-actin on a myosin coated hydrophobic cover glass and another assay of myosin coated beads along actin cables of Nitella. If a coefficient of 0.005 is applied to the kinetic friction, 1pN for the sliding force per cross-bridge and 10 microns sec-1 for the sliding speed, it is found that the bond strength between actin and one myosin head is about 200 pN in the contracting state.

Actomyosin↗

PubMed1991

Determination of the coefficient of kinetic friction of urinary catheter materials.

The coefficient of kinetic friction plays an important role in the biocompatibility of urinary catheters. A method for determination of the in vivo coefficient of kinetic friction is described that allows the comparison of the catheter-urethral interaction of the various materials used in the production of urinary catheters and the different types of lubricants.

Animals↗

PubMed2000

Shear force distance control in near-field optical microscopy: experimental evidence of the frictional probe-sample interaction

The properties of the probe-surface contact for a near-field optical microscope driven in the shear force mode have been studied applying lateral amplitudes of the probing fiber tip larger than 15 nm. Electric current measurements between a conductive tip and a conductive sample reveal a pulsed current behavior at the very beginning of the approach curve. In the upper part of the approach curve it turns to the quasiconstant current. From this observation a conclusion is drawn about the presence of permanent mechanical contact between the probe and the surface in the shear force mode. A shift of the approach curve along the z-axis as a function of dither amplitude was discovered. These results are in contradiction to the established conception of possible physical mechanisms of shear force interaction. To settle this issue the friction model is proposed according to which the damping of the probe vibrations is caused by the friction between the tip and the surface.

Journal Article↗

PubMed2002

Adhesion, friction, and mechanical properties of functionalized alkanethiol self-assembled monolayers.

We have used interfacial force microscopy to study the adhesion, friction, and mechanical properties of molecular monolayers self-assembled on Au surfaces. This quantitative and stable scanning-probe technique permits detailed studies of these factors. By systematic variation of the chemical nature of the end groups on the monolayers and utilization of standard and intuitive contact-mechanics models, quantitative results are presented of inter- and intrafilm bonding strength as well as the relationship between mechanical behavior and the lateral friction force.

Journal Article↗